Many pharmaceuticals are unstable when exposed to water vapor, and it is known that when the pharmaceuticals are left to stand unpacked, the quality is reduced by moisture absorption, thereby not exerting expected medicinal effects and besides causing side effects in a patient who took them. Therefore, most of the commercially available pharmaceuticals, especially solid formulations, are designed to avoid direct contact with water vapor by being packaged with a packaging material such as a PTP (press through pack) sheet. In recent years, PTP sheets in which polyvinylidene chloride, which has excellent water vapor barrier properties (moisture resistance), is laminated have been developed and put into practice.
Examples of methods for improving the stability of a solid formulation itself to water vapor include sugar-coating the solid formulation and film-coating the solid formulation with a macromolecular substance. In the latter, polyvinyl alcohol and aminoalkyl methacrylate copolymer E (Eudragit EPO (registered trademark); Degussa) are known as a macromolecular substance that exhibits water vapor barrier properties and, recently, a film coating agent having a capability of trapping water vapor in a coating layer by dispersing a hygroscopic drug in a water-soluble cellulose derivative (JP 2008-201712 A), a film coating agent having improved moisture resistance performance due to the addition of soybean lecithin, which is hydrophobic, to polyvinyl alcohol (U.S. Pat. No. 5,885,617), and a film coating agent having improved moisture resistance performance due to the addition of stearic acid to aminoalkyl methacrylate copolymer E (JP 2004-518750 W) have been developed.
In the field of packaging films different from the pharmaceutical field, a packaging film in which an inorganic layered compound is dispersed in polyvinyl alcohol is known as a means for improving the water vapor barrier performance under high humidity (JP 11-315222 A and JP 09-150484 A). However, it requires achieving only the moisture resistance, and it does not require considering the safety and disintegration properties as a pharmaceutical after being taken.
On the other hand, at clinical sites or dispensing pharmacies, to prevent forgetting to take prescribed drugs or taking a wrong dose, one-dose packages, which are provided by taking each of a plurality of pharmaceuticals to be taken in one dose out of a packaging material such as a PTP sheet and putting them in one bag, have been widespread and precedently used from a perspective different from the above-described approach to improve the stability of a solid formulation itself to water vapor by film coating, that is, from the standpoint of patient friendliness. In addition, in Western countries, patients often subdivide a pharmaceutical taken out of a package such as a PTP sheet for storage in a pill case or the like, and therefore methods for improving the water vapor barrier properties of a solid formulation itself have been demanded.
However, pharmaceuticals packed in a one-dose package, although their stability to water vapor is ensured at a distribution level by packaging materials such as a PTP sheet, can cause quality deterioration of the pharmaceuticals because they are stored unpacked for a long period of time, for example, at clinical sites.
When sugar-coating or conventional film-coating is applied to a solid formulation, quality deterioration due to water vapor might be reduced to some extent. However, at present, sugar-coating cannot be applied to all the solid formulations because the operation process takes a long time and because the solid formulation after sugar-coating can be so excessively large that it is difficult to take it; and sufficient water vapor barrier performance cannot be exhibited under high humidity even by the conventional film-coating. Further, a film coating agent in the field of packaging films has not been used as a pharmaceutical additive because it is a laminated film with a substrate film such as polyvinyl chloride, and at present it cannot be applied directly to a solid formulation from the standpoint of safety.
Thus, it could be helpful to provide a film coating agent for a solid formulation, which has excellent water vapor barrier properties and is capable of stably maintaining the quality of medicinal ingredients even when the solid formulation has been stored unpacked for a long period of time.